Radio system



Dec. 13, 1938. c. w. EARP RADIO SYSTEM Filed April 6, 1935 4 Sheets-Sheet l INVENTOR ATTORNEY c. 13,1938. EARP 2,140,130

' RADIO SYSTEM Q Filed April 6, 1935 4 Sheets-Sheet 4 DET- DET- l6 DET- /8 DET- l7" Ill DET-

ATTORNEY Patented Dec. 13, 1938 UNETED STTES RADIO SYSTEM Charles William Earp, Paris, France, assignor to Western Electric Company, Incorporated, New York, N. Y., a corporation of New York Application April 6, 1935, Serial No. 15,031 In France May 5, 1934 7 Claims.

This invention relates to radio frequency communication systems and particularly to directive radio systems.

As is well known, distortion and fading in radio communication often occur as the result of receiving from the distant station waves differing in phase as, for example, waves which possess different incoming directions in the same plane, and travel over paths of different lengths. Recently, a directive receiving system having means for manually adjusting the system to select or receive only a single wave included in an incoming plane wave cluster, and still more recently, a system having means for manually adjusting the antenna array to receive only the wave of maximum intensity, have been proposed for the purpose of eliminating distortion and fading. It is now realized that the direction of the maximum wave varies frequently during the communicating period and it appears desirable to adjust automatically the antenna directive characteristic in accordance with the directive changes in said Wave.

It is one object of this invention to improve radio communication.

It is another object of this invention to eliminate fading.

It is still another object of this invention to maintain efiicient directive communication between two stations either or both of which may be movable.

It is a further object of this invention to receive at a fixed or mobile station undistorted energy from only the wave of maximum intensity radiated by a given fixed or mobile station.

According to one feature of the present invention means are provided for adjusting the transmitter or receiver, or both, so that a change in the relative position of the transmitter or receiver, or in the path or paths followed by the signals transmitted, produces a compensating change at the receiving station. In other words, the principal lobe of the directive receiving characteristic of an antenna is automatically directed on the path over which the waves of maximum amplitude arrive.

According to one embodiment of the invention two antenna elements spaced to receive different components of the same incoming wave are connected to separate superheterodyne receivers which are associated with a common beat oscillator and a common second or final detector. Intermediate frequency current from one of the superheterodyne receivers is shifted 90 and supplied together with intermediate frequency current from the. other receiver to a push-pull detector. When out of phase components of the maximum wave are absorbed a positive or negative polarized current is produced in the output of the push-pull detector and this current is utilized to change the phase of the beat frequency current supplied to one of the receivers, whereby the intermediate frequency output of this receiver is changed in phase to compensate for the phase difference between the received components, and to produce at the second detector in-phase currents regardless of the phase relation of the absorbed wave components.

The invention will be more fully understood from the following specification taken in connection with the drawings, on which like reference characters designate elements of similar function and on which:

Fig. 1 illustrates one embodiment of the invention in which eight antennas are utilized, and Fig. 1A illustrates in detail the balanced detector included in the system illustrated by Fig. 1;

Fig. 2 illustrates a different embodiment in which only two antennas are employed;

Fig. 3 illustrates a modification of the system illustrated by Fig. 1;

Fig. 4 illustrates a communication system comprising movable stations and in which the invention may be employed; and

Fig. 5 illustrates the control transmitter employed at each of the movable stations in the system illustrated by Fig. 4.

Referring to Fig. 1A reference numerals I to 8, inclusive, designate antenna elements which may be horizontal or vertical, and either directional or non-directional. These elements are preferably but not necessarily positioned in the same plane and are preferably but not necessarily positioned or spaced the same distance apart. The term spaced elements is here defined as meaning elements or units physically separated and otherwise arranged to function independently of each other. The. spacing between adjacent elements is not critical and may be a few inches or several feet, but for convenience and economy is preferably in the order of a fractional wavelength. The elements l-8 are connected, respectively, to the first detectors designated by numerals H to l8. Reference numerals 2! to 28 designate harmonic generators which supply, respectively, beat frequency oscillations to the first detectors II to E8. One set of alternate antenna elements, that is, elements I, 3, 5 and I are each connected through the associated first detector to the input terminals of the intermediate frequency amplifier 9 and, similarly, elements 2, 4, 6 and 8 are each connected to the input terminals of the intermediate frequency amplifier ill. The two intermediate frequency amplifiers 9 and Ill are connected to the final detector or receiver 39. The outputs of intermediate frequency amplifiers 9 and ill are also connected to a detecting arrangement comprising intermediate or third detectors l9 and 20, amplifiers 29 and 30, beat oscillator 49 and balanced detector 50. The

these two resistances will be zero.

push-pull or balanced detector 58 is illustrated in detail by Fig. 1A. The beat oscillator 40 is connected directly to the detector 28 and through a quadrature phase shifter 5! to the detector Hi. The detecting arrangement just described is associated with a beat oscillator circuit comprising oscillator 52, 120 degree phase shifter 53, amlifiers 5 and 55, network 58 and an impedance comprising sections or arms 3! to 81, inclusive. The output circuit of the oscillator 52 is connected in parallel with the input circuits of each of the harmonic generators 2! to 28. The phase adjusting circuit is a series circuit comprising the input circuits of the harmonic generators 2| to 28 which are connected in eries with the impedance sections 3! to 37! at the points 4! to 48 and the output terminals of network 58.

Referring to Fig. 1A reference numerals 8D and 8! designate vacuum tubes connected in push-pull and each having a control electrode 82, an anode 83 and a heated cathode 84. For the sake of simplicity the means for heating the oathodes is not shown. Numerals 85 and 86 designate transformers connecting, respectively, amplifiers 88 and 28 to the input circuit of the push-pull detector 58, the connections being such that the energy from amplifier 30 is impressed in opposite phase on the control electrodes or grids 82 and the energy from amplifier 29 which is in quadrature to the energy from amplifier 3!! is impressed in similar phase on the grids 82. Numerals 8! designate radio frequency by-pass condensers, numerals 88 output resistances and numeral 89 a plate or anode battery. The two resistances 88 are connected in series with each other and in series with the input circuit of tube 98 included in amplifier 55, the input circuit including a grid biasing battery 9!, the grid or control electrode 82 and the cathode 84 of tube 9!]. From another viewpoint the two resistances 88 and the two anode-cathode impedances of tubes and 8! constitute a Wheatstone bridge.

In operation, it will be seen that the electromotive forces induced in the antenna elements to 8, inclusive, are received on the tuned grids of the detectors I! to I8, respectively, in which the frequency of the incoming signal components are changed. The various harmonic generators 2! to 28 all operate at the same frequency but these harmonic generators may operate with different phase. The intermediate frequency outputs of detectors H, !3, 5 and I! combine in amplifier 9 and the outputs of detectors l2, l4, l6 and !8 combine in the amplifier H]. The outputs of the amplifiers 9 and I!) are. applied in part to the ordinary receiver 39.

The manner in which the phases of the different harmonic generators 2! to 28 are automatically adjusted so that the system receives the waves coming from a single direction, which is the incoming direction of the maximum signals, will now be explained. Portions of the intermediate frequency outputs of amplifiers 9 and I!) are applied to detectors !9 and 20 where their frequency is changed by oscillator 48, the two outputs of which differ in phase by 90 degrees. If the outputs of amplifiers 9 and !E! are in phase, the output of detector 50 will be zero since the vector resultant of the quadrature components impressed on grid 82 of tube will have the same intensity as the resultant of the quadrature components impressed on grid 82 of tube 8!. In this case the oppositely directed currents in resistance series 88 will be equal and the potential across If, however,

they disagree in phase the outputs of amplifiers 29 and 38 will not be in quadrature and the vector resultant on grid 82 of tube 88 will decrease or increase while the vector resultant on grid 82 of tube 8i will change in an opposite sense. As a result a positive or negative polarized potential, dependent upon which extreme element, or 8, receives the leading wave component, will be present in the output of detector 50, and this potential increases or decreases the bias on the grid 82 of tube 9!] included in amplifier 55. Depending upon whether the polarized current increases or decreases the output of amplifier 55, the phase of the resulting current in the output of network 56 will be retarded or advanced. The phase of the current from network 56 applied to the impedances 3! to 31, will have a direction or sense depending upon which of elements I and 8 receives the leading wave component. The result'ant phase of the current from network 55 and the current from oscillator 52 as applied to the input circuit of each of the harmonic generators 2! to 28 will be such that the phase of the output current of the harmonic generators will. be changed an amount so as to compensate, in the case of any particular harmonic generator. for the difference in phase between the component absorbed by the associated element and the leading component as absorbed by an extreme element of the array. This is due in part to the fact that the impedances 3! to 37 are each proportioned to have the same electrical length as the spacing between the associated adjacent elements. Preferably, the harmonic generators 2! to 28 produce the hundredth harmonic of the frequency supplied by oscillator 52.

If the signals have a direction included in a plane perpendicular to the paper, the signals will add correctly in amplifiers 9 and I8 and zero current will be produced in the output of detector 58. If the direction of the maximum incoming wave changes, the phase relation of the input currents of detector 58 will change and this will. produce an unbalance which will automatically modify the phase relation between the harmonic generators. Consequently, as soon as a particular wave front has been received, this front will be followed even if its incoming direction changes. Similarly the maximum wave front will be followed in the case where it changes its direction in a plane including the paper, that is. including elements I to 8.

When the antenna system is of large dimension, it will be very directive and all the wave fronts except that which is desired will produce little effect on the receiver. If two wave fronts coincide in direction at any moment, they will both be employed and when they become separated, the receiver will follow the incoming path conveying the maximum signal. As a very wide frequency band is treated in a uniform manner when it travels in the same path and as directive changes in a single path are followed, general and selective fading will be automatically eliminated during the entire communication period.

Referring now to Fig. 2, a system constructed in accordance with the invention but in which only two antennas are employed will now be described. Reference numerals 28! and 202 designate antenna elements spaced at a convenient distance and each of which is connected to a superheterodyne receiver, element 2! being connected through first detector 2!! and intermediate frequency amplifier 22i and element 282 being connected through first detector 2I2 and intermediate frequency amplifier 222 to a common. final detector IEO. Reference numerals 23! and. 232 designate beat frequency oscillators which supply, respectively, first detectors 2!! and 2 l 2.

For the purpose of maintaining the frequency of. oscillator 23! equal to that generated by oscillator 232 a network comprising harmonic generators. 24! and 242, a detector 200 and an amplifier 203 is utilized. In the operation of this network. the twelfth harmonic of each of oscillators 23! and 232 is selected and applied to the detector 206. The current produced by this detector is amplified and applied to modify the impedance of a coil in the plate circuit of oscillator 23!, which coil is coupled to the tuning coil in beat oscillator 23!. The two harmonics from generators 24'! and 242 will be synchronized when there is a phase difference of 90 degrees inasmuch as any other phase relation will cause a corresponding change in the impedance coupled to the frequency determining circuit of oscillator 23! which change will alter the frequency generated until the 90 degree phase relation is reestablished. The oscillators may be synchronized. in any one of the twelve stable balancing positions included in the 360 degree cycle. In other words, the output of detector see changes the frequency of oscillator 23! until the oscillator finds thev necessary angle of phase to reestablish the balance.

Assuming oscillators 23! and 232 are generating the same frequency the phase of oscillator 23! is controlled in accordance with the direction of the incoming wave in a manner somewhat similar to that described in connection with Fig. 1. Either electrical or mechanical means may be utilized to control. the phase of oscillator 235. A satisfactory system comprises two coils in the output circuits of push-pull oscillator 23! positioned at right angles. A rotatable coil placed in the field. of these two coils delivers the energy to the. detector 2! I. The polarized current delivered over wire or connection i increases or decreases one of the stator fields and so controls the phase of the beat frequency current supplied to the detector 2! I. It will thus be seen that the phase and. the frequency of oscillator 23! are controlled, respectively, over wires or connections l0! and H32. The control effected by the connection I i]! does not change the phase of oscillator 23! in a' continuous manner. In order to avoid hunting when the path of the maximum wave varies rapidly, a delay network may be introduced in the connection !0!.

Referring to Fig. 3 a system is illustrated which is the same as that of Fig. 1 except that a simpler type of phase control circuit is employed. In the system of Fig. 3 the output of the intermediate frequency amplifier 9 is shifted 90 degrees and supplied with the intermediate frequency from amplifier Hi to the balanced detector 50. The polarized current obtained when differently phased components are absorbed by the elements I to 8, inclusive, controls by means of phase changer 54, the phase of one of the two outputs of the oscillator 52.

The system described above may be used for either transmitting or receiving purposes. In the case of the receiving system the directive lobe will follow the wave of maximum intensity, waves following another direction being minimized. In the case of the transmitting system.

the beam will be propagated in the direction of the receiving station, as determined by a direction finder at the transmitter. Moreover, the systems described above are useful in directionfinding and point-to-point communication systems in which the cooperating stations are fixed or movable as, for example, in ship-to-shore and ship-to-ship communication.

Fig. 4 illustrates two movable stations A and B operating in duplex. Each station is shown in two positions, the solid line illustration representing one position and the dotted line illustration representing the other position. Each station includes a receiving system 9! such as illustrated by Fig. 1, a direction finder 6! and transmitting system 92 of the type illustrated by Fig. 5 and now to be described.

Referring to Fig. 5 reference numeral 60 designates a loop connected to a direction finder 6! which controls through coil 62 a movable pointer 63. The transmitting system includes a Wheatstone bridge 64 having the four arm impedances W, X, Y and Z. The impedances W and X constitute one potentiometer 65 and impedances Y and Z constitute another potentiometer 66. The movable pointer 63 connected to an intermediate point on the potentiometer 65 determines the ratio of the position or setting of this pointer being determined or controlled by or direction finder 6! which is used for ascertaining the direction of the wave incoming from the other station. Similarly, the ratio is determined by a movable potentiometer pointer 61 which is actuated in either direction by a polarized motor 68. The polarized motor is connected between the two pointers on one diagonal of the bridge and a source of current 69 is included in the other diagonal. Beat frequency energy from the oscillator 52- is supplied through transformer 18 in phase to the two arms Y and Z and thence to the two primary windings H and 72 of transformer 13, the secondary winding 14 of which is connected in series with transformer coils l5 and resistances 16. Beat frequency energy is also supplied from oscillator 52 through transformer coils T! and 18 to the antenna elements I, 2, 3 and 4.

In operation when the ratio at station B changes as, for example, when the position of station A changes, the polarized motor adjusts the ratio until the bridge is balanced whereby the relative magnitudes of the oppositely phased or directed currents in the two primary transformer coils l! and 12 are changed. As a result the phase of the current in the transformer secondary winding 1 changes in sense and amount. Assuming the currents in coils l! and F2 are unequal and that the differently phased portions of the current from winding 74 combine in coils ll with similarly phased currents from coils 18 to produce differently phased antenna currents in elements I, 2, 3 and the direction of the beam transmitted from station B actually follows the movable. station A. At station A similar equipment is provided and the two stations are, in effect, linked together in a directive sense.

Although the invention has been explained in connection with certain specific embodiments, it should be understood that it is not limited to such embodiments. Obviously, other apparatus and arrays comprising either directive or nondirective units may be satisfactorily employed within the scope of the invention.

What is claimed is:

1. In combination, an antenna comprising at least three elements spaced in a line, a receiver connected to said elements, means connected to at least one pair of adjacent elements for obtaining a current representing the phase relation of the wave components absorbed by said pair of elements, and means controlled by said current for automatically and continuously producing in-phase currents at said receiver representing wave components absorbed by said elements, regardless of the incoming direction of the wave having said components.

2. In combination, an antenna array comprising at least three spaced elements adapted to receive different components of each of several waves incoming from a distant station, separate detectors connected to said elements, a common beat frequency oscillator connected to said detectors whereby output currents having equal intermediate frequencies and corresponding to the components of the maximum wave absorbed by said element are obtained, a single control means connected to all of said detectors for obtaining a single polarized current from said output currents representing the phase relation of the several components, phase shifting means included between said beat oscillator and said detectors and controlled by said polarized current for differently shifting the phase of the beat frequency currents supplied to said detectors, the phase of the beat frequency current supplied to a particular detector being shifted in sense and amount so as to compensate for the difference in phase between the component absorbed by the associated element and the leading component absorbed by an extreme element of the array.

3. In combination, a pair of cooperating radio stations comprising a transmitting system and a receiving system and arranged for relative movement with respect to each other, said receiving system comprising at least three antenna ele ments, a translation device, means comprising a single detector connected to all of said elements for obtaining a current representing the phase relation of the wave components absorbed by two adjacent elements, and means controlled by said current for automatically and continuously during the communicating period producing at said device a plurality of in-phase currents from the maximum wave received from said transmitting system regardless of changes in the incoming direction of said wave.

4. A directive radio receiving system comprising a plurality of absorbing elements evenly spaced in a line, separate first detectors connected thereto, a common beat frequency oscillator, a plurality of equal frequency harmonic generators, the output circuit of said oscillator being connected in parallel with the input circuit of each harmonic generator and through a different harmonic generator to each first detector, two intermediate frequency amplifiers, the detectors connected to a set of alternate absorbing elements being connected to one of the posite phase whereby a current having a polarity and intensity dependent upon the direction of the maximum incoming wave is obtained when said output energies are dissimilar in resultant phase, a first control amplifier connected directly and a second control amplifier connected through a phase shifter to the output of the oscillator, said phase shifter being adapted to alter the phase of this current an amount other than 180 degrees or a multiple thereof, said second control amplifier being controlled by the polarized current, a network for combining the output of said control amplifiers, a series circuit including the output terminals of said network, the input terminals of said harmonic generators, and a plurality of impedances the electrical length of each of which is equivalent to the spacing between adjacent elements and a difierent one of which is serially included between the input circuits of harmonic generators associated with adjacent absorbing elements.

5. A method of improving radio communication which comprises receiving a plurality of wave components, producing from all of said components a control current representing the phase difference of said components, modulating each wave component with a distinct locally generated current, causing said control current to adjust the phase relation of all said locally generated currents in the proper sense and degree to compensate for the phase difference of the wave components, whereby in-phase modulated currents are obtained, and translating said modulated currents.

6. In combination, an antenna array comprising at least three elements, an oscillator, separate detectors for combining the wave components absorbed by each element with different currents from said oscillator, means for deriving from all of the detected currents a single control current having an intensity and polarization sense corresponding to the phase difference between the components absorbed by two adjacent elements, and means for adjusting the phase of the oscillator currents supplied to the detectors associated'with said adjacent elements in accordance with said control current.

7. In combination, an antenna array comprising at least three elements, a beat frequency oscillator, separate detectors connected between said oscillator and said elements, means for obtaining from all of the detected currents a single control current when out-of-phase components are absorbed by said elements, and means controlled by said control current and included between said oscillator and detectors for rendering the waves supplied by said oscillator to the detectors connected to adjacent elements differentin phase by an amount related to the difference in phase of the wave components absorbed by said adjacent elements, whereby the detected currents are rendered in phase.

CHARLES WILLIAM EARP. 

